Patellar/Kneecap Dislocation

Overview

Patellar dislocation is when the kneecap moves out of its normal position. This could happen because of a twisting injury to the knee or when the kneecap is hit directly. This may be predisposed when there is an imbalance in the muscle on the inside (vastus medialis) and the muscle on the outside (vastus lateralis). In several cases there may be an anatomical variation i.e. the Q Angle may be large, or the trochlear groove may not be well formed.

Symptoms

The knee is painful and held in a bent position, there may be swelling and the person may not be able to walk.

Investigations

X-Ray – The kneecap may be out of place if it is not reduced.
X-Ray may show a shallow trochlear groove if not well formed and also an increased Q Angle.
MRI Scan – These magnetic scans are used for diagnosis of soft tissue, cartilages and bony pathology. This may also show any loose bony fragment.

Treatment

Non-operative
The kneecap needs to be reduced in the emergency department. Thereafter a splint is applied to rest the knee. Physiotherapy will help reduce the swelling, pain and also strengthen the muscles and regain range of motion.

Operative

If there is recurrent dislocation of the kneecap and physiotherapy has not helped, surgery may be considered.

Depending on the underlying cause surgery may vary from:

Reconstruction of the MPFL (medial patellar femoral ligament).
Tibial tuberosity transfer, if it is found on a CT Scan / MRI Scan that the TT – TG distance (tibial tuberosity – tibial groove) to be more than normal.
If the trochlear groove is shallow then deepening of the groove may be considered.